Update Flow with support for "configuration" on Sequence nodes

[bhouston]

Some nodes now support "configuration". This is for non-run-time configuration of nodes, right now that exclusively deals with changing the actual socket structure of the nodes.

The first few nodes I've applied this to are: (1) Sequence, (2) WaitAll, (3) Custom Event Trigger and (4) On Custom Event. There is also a PR for (5) Switch.

We now need to update the Flow library to handle modifying nodes by changing their configuration.

For example for Sequence, we have to increase/decrease the "numOutputs" of the configuration and then recreate the node and replace the existing node with this new version. When replacing the node with the new version, we should aim to keep as many of the existing connections as possible.

I think we probably need to make custom UI elements for each of these nodes that has configuration parameters? Or maybe we can formalize it so that we can auto-create UI elements for them?

What do people think?

[bhouston]

This was implemented and merged.